JP5505230B2 - Optical semiconductor device - Google Patents

Description

  The present invention relates to an optical semiconductor element.

  In recent years, an optical transmitter in which a semiconductor laser and a Mach-Zehnder interferometer type optical modulator (hereinafter also simply referred to as an MZ optical modulator) are combined has been developed. This type of optical transmitter is used, for example, in a wavelength division multiplexing transmission system. Further, there is a demand for a small optical transmitter.

As the MZ light modulator, for example, there is an MZ light modulator (hereinafter, also simply referred to as an LN-MZ light modulator) using an electro-optic effect of lithium niobate (LiNbO ₃ : LN) which is a nonlinear optical crystal. The LN-MZ optical modulator has a wide operating wavelength band and can be chirped. Then, it has been proposed to combine a semiconductor laser and an LN-MZ optical modulator together with optical components such as a lens and an isolator and integrate them in the same module to reduce the size of the optical transmitter.

  However, the size of the optical transmitter is limited by the large size of the LN-MZ optical modulator itself and the combination of a plurality of optical components such as a lens and an isolator.

  In addition, by using a planar lightwave circuit (PLC) element formed of a quartz-based material, a semiconductor laser and an LN-MZ optical modulator are integrated in a hybrid manner, thereby further reducing the size of the optical transmitter. It has been proposed to

  However, such an optical transmitter is difficult to manufacture because it is not easy to optically couple the formed parts.

  An optical semiconductor element in which a semiconductor Mach-Zehnder interferometer type optical modulator (hereinafter also referred to as a semiconductor MZ optical modulator) using a semiconductor having a lattice constant comparable to that of the substrate is formed on the same substrate on which the semiconductor laser is formed. Has been proposed. In this case, the semiconductor laser, the semiconductor MZ optical modulator, and the optical waveguide connecting them are linearly arranged on the same substrate. In this optical semiconductor device, the semiconductor laser and the semiconductor MZ optical modulator can be manufactured in-line on the same substrate.

  In the semiconductor MZ optical modulator, in particular, in a semiconductor MZ optical modulator using a quantum confined stark effect (QCSE) that changes the refractive index by applying an electric field to the quantum well structure, LN-MZ light is used. Compared with the modulator, the amount of change in the refractive index is large. Therefore, the semiconductor MZ optical modulator is expected to reduce the size and driving voltage of the optical semiconductor element.

  When the semiconductor laser is a Fabry-Perot laser or a distributed feedback (DFB) laser, the element length of the laser is about several hundred μm. On the other hand, in the case of a semiconductor laser in which the wavelength of the output light is variable, particularly in the case of a wavelength variable semiconductor laser having a wide wavelength variable band, the element length of the laser may be several mm.

  In addition, since the combined length of the optical coupler, the optical waveguide, and other elements such as the phase modulation unit is about several millimeters, the semiconductor laser and the semiconductor MZ optical modulator are arranged linearly, The longitudinal dimension of the optical semiconductor element is increased. The optical branching device described above is a forming element for branching input light into two optical waveguides in the MZ optical modulator. However, the optical branching device has variations in optical branching characteristics due to variations in manufacturing processes. Therefore, the optical branching ratio at which the input light is branched into the two optical waveguides may deviate from equal branching.

  Furthermore, the large size of the optical semiconductor element in the longitudinal direction reduces the number of elements that can be manufactured from a single substrate, and the increase in the aspect ratio (aspect ratio) of the element means that the yield in the manufacture of the element. It can also be a cause of lowering.

  Therefore, it is expected to reduce the size of the optical semiconductor element provided with the semiconductor laser and the semiconductor MZ optical modulator.

JP 2009-198881 A JP 2004-22618 A JP-A-2005-159118 JP 2004-53830 A JP 2007-93717 A JP 2009-146992 A

  The present specification aims to provide an optical semiconductor device with reduced dimensions.

  In order to solve the above problems, according to one embodiment of an optical semiconductor element disclosed in this specification, a semiconductor laser that is formed on a substrate and outputs light from each of opposing ends, and a semiconductor laser that is formed on the substrate A first phase modulation unit having a first optical waveguide to which output light from one end of the semiconductor laser is input, and a second optical waveguide formed on the substrate and to which output light from the other end of the semiconductor laser is input And a second phase modulator having an optical coupler and an optical coupler that is formed on the substrate and that combines and outputs the output light from the first optical waveguide and the second optical waveguide.

  According to one embodiment of the optical semiconductor element disclosed in the present specification described above, the size is reduced.

  The objects and advantages of the invention will be realized and obtained by means of the elements and combinations particularly pointed out in the appended claims.

  Both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention as claimed.

1 is a diagram illustrating a first embodiment of an optical semiconductor device disclosed in this specification. FIG. It is an AA line expanded sectional view of FIG. It is a BB line expanded sectional view of Drawing 1. It is the C-C 'line expanded sectional view of FIG. (A) is an enlarged view of the main part of FIG. 1, (B) shows the intensity distribution of light propagating through the core layer embedded in the first embedded layer, and (C) shows the second embedded layer. The intensity distribution of the light which propagates the core layer embedded in the layer is shown. It is FIG. (The 1) which shows the manufacturing process of the optical semiconductor element of 1st Embodiment. It is FIG. (2) which shows the manufacturing process of the optical semiconductor element of 1st Embodiment. FIG. 8 is a view (No. 3) showing a manufacturing step of the optical semiconductor element of the first embodiment, which is an enlarged cross-sectional view taken along the line D-D ′ of FIG. It is FIG. (The 4) which shows the manufacturing process of the optical semiconductor element of 1st Embodiment. FIG. 10 is a view (No. 5) showing a manufacturing step of the optical semiconductor element of the first embodiment, which is an enlarged sectional view taken along line E-E ′ of FIG. 9; It is FIG. (6) which shows the manufacturing process of the optical semiconductor element of 1st Embodiment. It is FIG. (The 7) which shows the manufacturing process of the optical semiconductor element of 1st Embodiment. FIG. 13 is a view (No. 8) showing a manufacturing step of the optical semiconductor element of the first embodiment, which is an enlarged sectional view taken along line FF in FIG. 12; FIG. 13 is a drawing (No. 9) showing a manufacturing step of the optical semiconductor element of the first embodiment, which is an enlarged sectional view taken along the line GG of FIG. 12; It is FIG. (10) which shows the manufacturing process of the optical semiconductor element of 1st Embodiment. It is a figure (the 11) which shows the manufacturing process of the optical semiconductor element of 1st Embodiment, and is the HH line expanded sectional view of FIG. FIG. 16 is a view (No. 12) illustrating a process for manufacturing the optical semiconductor element of the first embodiment, which is an enlarged cross-sectional view taken along the line II of FIG. 15; It is FIG. (13) which shows the manufacturing process of the optical semiconductor element of 1st Embodiment. It is FIG. (14) which shows the manufacturing process of the optical semiconductor element of 1st Embodiment. It is FIG. (15) which shows the manufacturing process of the optical semiconductor element of 1st Embodiment. It is FIG. (16) which shows the manufacturing process of the optical semiconductor element of 1st Embodiment. It is a figure which shows the modification 1 of the optical semiconductor element of 1st Embodiment. It is a figure which shows the modification 2 of the optical semiconductor element of 1st Embodiment. It is a figure which shows 2nd Embodiment of the optical semiconductor element disclosed to this specification. It is a figure which shows the relationship between a phase modulation voltage, a phase change amount, and a loss amount. It is a figure which shows 3rd Embodiment of the optical semiconductor element disclosed in this specification. It is a figure which shows 4th Embodiment of the optical semiconductor element disclosed by this specification. It is the J-J 'line expanded sectional view of FIG.

  Hereinafter, a preferred first embodiment of an optical semiconductor device disclosed in this specification will be described with reference to the drawings. However, it should be noted that the technical scope of the present invention is not limited to these embodiments, but extends to the invention described in the claims and equivalents thereof.

  FIG. 1 is a diagram showing a first embodiment of an optical semiconductor device disclosed in this specification. FIG. 2 is an enlarged cross-sectional view taken along line AA in FIG. FIG. 3 is an enlarged sectional view taken along line BB in FIG.

  The optical semiconductor element 10 of the present embodiment includes a semiconductor laser 11 that is formed on a semiconductor substrate 30 and outputs light from each of opposite ends in the longitudinal direction. In addition, the optical semiconductor element 10 includes a first phase modulation unit 12 having a first optical waveguide 12a to which output light from one end in the longitudinal direction of the semiconductor laser 11 is input. The optical semiconductor element 10 further includes a second phase modulation unit 13 having a second optical waveguide 13a to which output light from the other end in the longitudinal direction of the semiconductor laser is input. The first phase modulation unit 12 and the second phase modulation unit 13 are formed on the substrate 30 together with the semiconductor laser 11.

  In addition, the optical semiconductor element 10 includes an optical coupler 15 that is formed on the substrate 30 and that combines and outputs output light from the first optical waveguide 12a and the second optical waveguide 13a.

  The first phase modulation section 12 includes a first phase modulation electrode 12b that changes the refractive index of the optical waveguide by applying a modulation electric field to the first optical waveguide 12a together with the first optical waveguide 12a. The first optical waveguide 12a is formed in a straight vertically long shape. The first phase modulation electrode 12b is vertically long and covers the entire longitudinal direction of the first optical waveguide 12a. As shown in FIG. 1, the first phase modulation section 12 is vertically long, and the longitudinal direction thereof coincides with the longitudinal directions of the first optical waveguide 12a and the first phase modulation electrode 12b. The phase of light propagating through the first optical waveguide 12a changes in accordance with the refractive index of the optical waveguide. As shown in FIG. 3, the first phase modulation electrode 12b is disposed above the first optical waveguide 12a.

  The second phase modulation unit 13 includes a second phase modulation electrode 13b that applies a modulation electric field to the second optical waveguide 13a together with the second optical waveguide 13a. The structure of the second phase modulation unit 13 is the same as that of the first phase modulation unit 12 described above.

  The longitudinal directions of the first phase modulation unit 12 and the second phase modulation unit 13 coincide with the longitudinal direction of the optical semiconductor element 10.

  The first phase modulation unit 12 and the second phase modulation unit 13 are arranged in parallel with a separation in the width direction. Here, the width direction is a direction orthogonal to the longitudinal direction of the first optical waveguide 12a and the second optical waveguide 13a. In the optical semiconductor element 10, the first optical waveguide 12a and the second optical waveguide 13a have the same length.

  Next, the semiconductor laser 11 will be further described.

  As shown in FIGS. 1 and 2, the semiconductor laser 11 includes a laser mesa unit 11a and a laser drive electrode 11b that injects a drive current into the laser mesa unit 11a. As shown in FIG. 1, the laser drive electrode 11b is vertically long and covers the entire length of the laser mesa portion 11a. As shown in FIG. 2, the laser drive electrode 11b is disposed above the laser mesa unit 11a.

  The semiconductor laser 11 is disposed on one end side in the longitudinal direction of the first phase modulation unit 12 and the second phase modulation unit 13. The first phase modulation unit 12 and the second phase modulation unit 13 are arranged in parallel with their longitudinal directions matched. The semiconductor laser 11 is arranged between the first phase modulation unit 12 and the second phase modulation unit 13, and the longitudinal direction of the semiconductor laser 11 is the same as that of the first phase modulation unit 12 and the second phase modulation unit 13. Intersects the longitudinal direction. Specifically, the longitudinal direction of the semiconductor laser 11 and the longitudinal directions of the first phase modulation unit 12 and the second phase modulation unit 13 are orthogonal to each other.

  The distance between the end of the semiconductor laser 11 in the longitudinal direction and the first phase modulation unit 12 or the second phase modulation unit 13 is the distance between the laser drive electrode 11b and the first phase modulation electrode 12b or the second phase modulation electrode 13b. It is preferable that the crosstalk does not occur between them. For example, the distance between the semiconductor laser 11 and the first phase modulation unit 12 or the second phase modulation unit 13 can be set to 100 to 200 μm.

  The semiconductor laser 11 is preferably a single mode laser. The semiconductor laser 11 may be a wavelength tunable laser. Specifically, the semiconductor laser 11 includes a distributed feedback (DFB) type laser, a distributed Bragg reflection (DBR) type laser, a super structure grating (SSG) type DBR laser, and the like. Alternatively, a CSG-DR (Chirped Sampled Distributed Distributor) type laser may be used.

  In the present embodiment, the following description is given by taking the case where the semiconductor laser 11 is a DFB type laser as an example.

  Next, the cross-sectional structure of the semiconductor laser 11 will be described below with reference to the drawings.

  As shown in FIG. 2, the semiconductor laser 11 includes a laser mesa portion 11a formed on the substrate 30 and a laser drive electrode 11b formed thereon.

  The laser mesa unit 11 a includes a lower cladding layer 31 disposed on the substrate 30, a diffraction grating layer 32 disposed on the lower cladding layer 31, a spacer layer 33 disposed on the diffraction grating layer 32, and a spacer layer 33. And a core layer 34 of the semiconductor laser disposed on the semiconductor laser. A diffraction grating having periodicity in the light propagation direction is formed on the diffraction grating layer 32 of the laser mesa unit 11a. In addition, a λ / 4 phase shift is formed at the center in the longitudinal direction of the diffraction grating layer 32 in the laser mesa unit 11a. A DFB type laser having a λ / 4 phase shift in the diffraction grating layer can equalize the light intensity output from both ends in the longitudinal direction. The laser mesa unit 11a includes a first upper cladding layer 36 disposed on the core layer 34 of the semiconductor laser, a third upper cladding layer 38 disposed on the first upper cladding layer 36, and a third upper cladding layer. And a first contact layer 39 disposed on 38. Further, the portion of the substrate 30 located under the lower cladding layer 31 also forms part of the laser mesa portion 11a.

  The laser drive electrode 11 b includes a first electrode 40 and a second electrode 41. The laser drive electrode 11b is electrically connected to the laser mesa unit 11a through the first electrode 40 and the second electrode 41.

  The laser mesa unit 11 a is embedded by the first embedded layer 42. A first passivation layer 43 is disposed on the first buried layer 42, a second buried layer 44 is disposed on the first passivation layer 43, and a second passivation layer 45 is disposed on the second buried layer 44. Is done. The lower side of the laser drive electrode 11 b is buried with the second buried layer 44.

  The laser mesa unit 11a receives current injection from the laser drive electrode 11b, oscillates laser light, generates heat, and thermally expands. The first buried layer 42 is also heated by the laser mesa unit 11a and thermally expands. Therefore, it is preferable that the laser mesa portion 11a and the first buried layer 42 have no difference in thermal expansion coefficient in order to prevent thermal stress from being generated in the laser mesa portion 11a or the first buried layer 42. If thermal stress is generated in the laser mesa unit 11a or the first buried layer 42, the life of the semiconductor laser 11 may be shortened due to generation of cracks or the like.

  For example, the difference between the thermal expansion coefficients of the first buried layer 42 and the core layer 34 of the semiconductor laser is preferably within ± several% from the viewpoint described above. The material for forming the first buried layer 42 is preferably formed using a semiconductor similar to the substrate. The first buried layer 42 preferably has semi-insulating conductivity in order to increase the efficiency of current injection into the core layer 34.

  In FIG. 1, a region where the first buried layer 42 is formed is shown as a first buried region B1. In the first buried region B1, the semiconductor laser 11 is buried with the first buried layer. In addition, in the first embedded region B1, portions on the input side of a first bent optical waveguide 17a and a second bent optical waveguide 17b, which will be described later, are embedded with a first embedded layer.

  Next, the cross-sectional structure of the first phase modulation unit 12 will be described below with reference to the drawings.

  As shown in FIG. 3, the first optical waveguide 12a of the first phase modulator 12 has a mesa structure.

  The first optical waveguide 12a has the same structure as the laser mesa 11a of the semiconductor laser 11 except for the following points. In the first optical waveguide 12 a, no diffraction grating is formed in the diffraction grating layer 32. An optical waveguide core layer 35 is disposed on the spacer layer 33, and a second upper clad layer 37 is disposed on the optical waveguide core layer 35. Further, both side surfaces of the first optical waveguide 12 a are covered with the first passivation layer 43. The first passivation layer 43 also covers the substrate 30 on both sides of the first optical waveguide 12a. A first phase modulation electrode 12b is disposed on the first optical waveguide 12a. The lower portion of the first phase modulation electrode 12 b is embedded with the second embedded layer 44.

  The first optical waveguide 12a is embedded with a second embedded layer 44 having a lower refractive index than the core layer 35 of the first optical waveguide 12a. From the viewpoint of confinement of light propagating through the first optical waveguide 12a, the difference between the refractive index of the second buried layer 44 and the refractive index of the core layer 35 of the first optical waveguide is preferably large.

  As a material for forming the second embedded layer 44, for example, a resin having a low dielectric constant or air can be used.

  The second phase modulation unit 13 has the same cross-sectional structure as the first phase modulation unit 12, and the above description is also applied to the second phase modulation unit 13 as appropriate.

  In FIG. 1, a region where a mesa structure such as an optical waveguide is embedded by the second embedded layer 44 is shown as a second embedded region B2. In the second embedded region B2, the first optical waveguide 12a, the second optical waveguide 13a, and the optical coupler 15 are embedded by the second embedded layer 44. In the second embedded region B2, the output side portions of a first bent optical waveguide 17a and a second bent optical waveguide 17b, which will be described later, are embedded by the second embedded layer 44.

  Further, on the back side of the substrate 30, lower electrodes (not shown) are arranged corresponding to the laser drive electrode 11 b and the first and second phase modulation electrodes 12 b and 13 b.

  Next, the first bent optical waveguide 17a that receives and bends the output light from one end of the semiconductor laser 11 and propagates the light to the first optical waveguide 12a will be described below with reference to the drawings.

  As shown in FIG. 1, the optical semiconductor element 10 includes a first bent optical waveguide 17 a formed on a substrate 30. The first bent optical waveguide 17a receives the output light of the semiconductor laser 11, and propagates the light by bending the propagation direction by 90 degrees. Thus, the optical semiconductor element 10 propagates light from the semiconductor laser 11 arranged in the orthogonal direction to the first optical waveguide 12a using the first bent optical waveguide 17a.

  Next, a cross-sectional structure of a joint portion between the first bent optical waveguide 17a and the semiconductor laser 11 will be described below with reference to the drawings.

  FIG. 4 is an enlarged sectional view taken along line C-C ′ of FIG. 1. FIG. 4 shows a cross-sectional structure in the longitudinal direction at the junction between the first bent optical waveguide 17 a and the semiconductor laser 11.

  As shown in FIG. 4, the first bent optical waveguide 17a has the same structure as the first optical waveguide 12a described above except for the following points. In the first bent optical waveguide 17a, the first phase modulation electrode 12b is not disposed. Further, the first contact layer 39 is covered with a first passivation layer 43.

  At the junction between the first bent optical waveguide 17a and the semiconductor laser 11, a junction interface S1 between the core layer 35 of the optical waveguide and the core layer 34 of the semiconductor laser is formed. The joining interface S1 is a so-called butt joint interface. Further, at the position of the junction interface S1, the junction interface between the first upper cladding layer 36 disposed on the core layer 34 of the semiconductor laser and the second upper cladding layer 37 disposed on the core layer 35 of the optical waveguide. Is also formed.

  The core layer 35 of the optical waveguide extends on an arc toward the first optical waveguide 12a from the junction interface S1, which is the end face of the core layer 34 of the linear semiconductor laser.

  The radius of curvature of the first bent optical waveguide 17a can be determined so as to ensure a preferable separation distance between the semiconductor laser 11 and the first phase modulator 12 described above. Further, the lower limit value of the radius of curvature of the first bent optical waveguide 17a may be restricted in the manufacturing process. From such a viewpoint, the radius of curvature of the first bent optical waveguide 17a can be set to 100 μm, for example.

  Further, as shown in FIG. 1, the input-side portion of the first bent optical waveguide 17a is included in the first embedded region B1 similarly to the laser mesa portion 11a.

  On the other hand, as shown in FIG. 1, the output side portion of the first bent optical waveguide 17a connected to the first optical waveguide 12a is included in the second embedded region B2, and is in the middle of the first bent optical waveguide 17a. A junction interface S2 between the first buried layer 42 and the second buried layer 44 is formed at the position.

  Next, the position of the bonding interface S2 between the first buried layer 42 and the second buried layer 44 will be described below with reference to the drawings.

  FIG. 5A is an enlarged view of a main part of FIG. FIG. 5B shows the intensity distribution of light propagating through the core layer 35 embedded in the first embedded layer 42. FIG. 5C shows the intensity distribution of light propagating through the core layer 35 embedded in the second embedded layer 44.

  FIG. 5A shows a portion of the first bent optical waveguide 17a extending on the arc from the bonding interface S1 of the laser mesa portion 11a. In FIG. 5A, a bonding interface S2 formed at a position P in the middle of the first bent optical waveguide 17a is indicated by a one-dot chain line. FIG. 5A shows a tangent line L1 at the position P of the arc-shaped first bent optical waveguide 17a. Further, in FIG. 5A, the straight traveling direction of the light output from the bonding interface S1 is indicated by a straight line L2.

  The position P in the middle of the first bent optical waveguide 17a where the bonding interface S2 is formed is determined by the angle α formed by the tangent line L1 and the straight line L2. The angle α is also the central angle of the arc formed by the position of the bonding interface S1 and the position P around the center of curvature O of the first bent optical waveguide 17a.

  As shown in FIG. 5B, in the portion of the first bent optical waveguide 17a embedded in the first embedded layer 42, the intensity distribution of light propagating through the core layer 35 of the mesa portion 17aa of the first bent optical waveguide 17a. Extends beyond the width of the core layer 35. On the other hand, as shown in FIG. 5C, in the portion of the first bent optical waveguide 17a embedded in the second embedded layer 44, the intensity distribution of the light propagating through the core layer 35 is within the width of the core layer 35. Almost confined.

  When light having an intensity distribution as shown in FIG. 5 (B) passes through the junction interface S2, the light is reflected by the junction interface S2 having a different equivalent refractive index, and the first bent optical waveguide 17a toward the semiconductor laser 11 is obtained. Light that returns inside is generated.

  Therefore, in the optical semiconductor element 10, the junction interface S2 between the first buried layer 42 and the second buried layer 44 is formed at a position in the middle of the first bent optical waveguide 17a, and the first semiconductor laser 11 is reflected by reflection. The amount of light returning through the bent optical waveguide 17a is reduced.

  The amount of light that returns to the semiconductor laser 11 by reflection and returns in the optical waveguide 17a decreases as the value of the angle α that determines the position P of the bonding interface increases.

  On the other hand, the upper limit of the angle α may be determined due to restrictions on the manufacturing process. For example, when the angle α increases, the first buried layer 42 may grow so as to rise on the mesa structure of the first bent optical waveguide 17a. In such a case, the angle α is preferably set to a size within a range where the first buried layer 42 does not grow abnormally.

  Therefore, in the present embodiment, the angle α is set to an upper limit value at which the first embedded layer 42 does not grow abnormally when the mesa structure of the first bent optical waveguide 17a is embedded. In this way, by determining the angle α, the position P of the bonding interface S2 between the first buried layer 42 and the second buried layer 44 is determined. For example, the angle α may be 10 degrees.

  In addition, the optical semiconductor element 10 includes a second bent optical waveguide 17b that receives the output light from the other end in the longitudinal direction of the semiconductor laser 11 and curves the light to propagate the light to the second optical waveguide 13a. The second bent optical waveguide 17b has the same structure as the first bent optical waveguide 17a. Therefore, the above description for the first bent optical waveguide 17a is also applied to the second bent optical waveguide 17b as appropriate.

  Next, the optical coupler 15 will be described. The optical coupler 15 causes the input two lights to interfere with each other and outputs light having a light intensity corresponding to the phase difference. As the optical coupler 15, for example, a multimode interference coupler having two input ports and two output ports can be used. The cross-sectional structure of the optical coupler 15 is the same as that of the first bent optical waveguide 17a described above. Note that a multimode interference coupler having two input ports and one output port may be used as the optical coupler 15.

  As shown in FIG. 1, the optical semiconductor element 10 is formed on the substrate 30, receives the output light of the first optical waveguide 12 a, bends the propagation direction, and propagates the light to the optical coupler 15. An optical waveguide 18a is provided. The optical semiconductor element 10 includes a fourth bent optical waveguide 18b that is formed on the substrate 30 and receives the output light of the second optical waveguide 13a, bends the propagation direction, and propagates the light to the optical coupler 15.

  The optical semiconductor element 10 includes fifth and sixth optical waveguides 19 a and 19 b that input light from the output port of the optical coupler 15 and output light to the outside. The exposed end faces of the fifth and sixth optical waveguides 19a and 19b are preferably coated with antireflection, for example.

  The cross-sectional structures of the third and fourth bent optical waveguides 18a and 18b and the fifth and sixth optical waveguides 19a and 19b are the same as those of the first bent optical waveguide 17a described above.

  In the above-described second embedded region B2, the third and fourth bent optical waveguides 18a and 18b and the fifth and sixth optical waveguides 19a and 19b are embedded by the second embedded layer 44.

  Further, the first phase modulation unit 12 and the second phase modulation unit 13, the optical coupler 15, the third and fourth bent optical waveguides 18a and 18b, the fifth and sixth optical waveguides 18a and 18b, As a result, a semiconductor optical modulator is formed on the same substrate 30.

  Next, an example of a preferable method for manufacturing the above-described optical semiconductor element 10 of the present embodiment will be described below with reference to the drawings.

  First, as shown in FIG. 6, the lower cladding layer 31 is formed on the substrate 30. As a method for forming the lower cladding layer 31, for example, epitaxial growth by metal organic chemical vapor deposition (MOCVD) can be used. Similarly, the diffraction grating layer 32 to the first upper cladding layer 36 to be described later can also be formed using the MOCVD method. For example, n-InP can be used as a material for forming the substrate 30. For example, the lower cladding layer 31 can be made to have a thickness of 200 nm by using n-InP as a forming material.

  A diffraction grating layer 32 is formed on the lower cladding layer 31. As a material for forming the diffraction grating layer 32, for example, n-InGaAsP having a composition wavelength of 1.2 μm can be used. The thickness of the diffraction grating layer 32 can be set to, for example, 70 nm. In addition, a diffraction grating having a period of about 240 nm in the light propagation direction is formed in the region of the diffraction grating layer 32 to be a semiconductor laser by using electron beam (EB) exposure and dry etching, for example. In addition, a λ / 4 phase shift is formed in the central portion in the longitudinal direction of the region of the diffraction grating layer 32 that becomes the semiconductor laser. Note that a diffraction grating is not formed in a region of the diffraction grating layer 32 that does not become a semiconductor laser.

  Then, the spacer layer 33 is formed on the diffraction grating layer 32. For example, the spacer layer 33 can be made to have a thickness of 100 nm by using n-InP as a forming material.

  Then, the core layer 34 of the semiconductor laser is formed on the spacer layer 33. The core layer 34 is formed by a multilayer quantum well (MQW) active layer and SCH layers disposed above and below the MQW active layer. The MQW active layer is formed by, for example, using i-InGaAsP as a forming material and laminating a barrier layer having a thickness of 15 nm and a well layer having a thickness of 5 nm by eight periods, and a PL emission wavelength of 1.55 μm. can do. A barrier layer is disposed inside each SCH layer. For example, i-InGaAsP having a composition wavelength of 1.15 μm is used as a forming material, and the thickness of the SCH layer can be 12.5 nm.

  A first upper cladding layer 36 is formed on the core layer 34 of the semiconductor laser. For example, the first upper cladding layer 36 can be made to have a thickness of 200 nm by using p-InP as a forming material.

Next, as shown in FIG. 7, a patterned first mask layer M <b> 1 is formed on the region of the first upper cladding layer 36 that becomes a semiconductor laser by using a technique such as photolithography. For the first mask layer M1, for example, SiO ₂ can be used as a forming material. As a method for forming the first mask layer M1, for example, a chemical vapor deposition (CVD) method can be used.

  Next, as shown in FIG. 8, using the first mask layer M1 as a mask, the first upper cladding layer 36 and the core layer are formed on the region where the first mask layer M1 is not formed using wet etching or the like. 34 is selectively removed and the spacer layer 33 is exposed.

  Next, as shown in FIGS. 9 and 10, using the first mask layer M1 as a selective growth mask, the core layer 35 of the optical waveguide on the spacer layer 33 in the region where the first mask layer M1 is not formed, The second upper cladding layer 37 is formed in order. As a method for forming the core layer 35 and the second upper cladding layer 37, for example, epitaxial growth by MOCVD method can be used. For example, the core layer 35 may be made of i-InGaAsP having a composition wavelength of 1.38 μm as a forming material and may have a thickness of 200 nm. The second upper cladding layer 37 can be made to be 200 nm in thickness by using p-InP as a forming material. In this way, the core layer 35 of the optical waveguide is butt-joint grown with respect to the core layer 34 of the semiconductor laser to form a bonding interface S1 between the core layer 35 of the optical waveguide and the core layer 34 of the semiconductor laser. Then, the first mask layer M1 is removed.

  Further, in the future, the optical waveguide structure including the core layer 35 of the optical waveguide has the first bent optical waveguide 17a and the second bent optical waveguide 17b, the first and second optical waveguides 12a and 13a, the optical coupler 15, The optical waveguide structures of the third and fourth bent optical waveguides 18a and 18b and the fifth and sixth optical waveguides 19a and 19b are formed.

  Next, as shown in FIG. 11, a third upper cladding layer 38 and a first contact layer 39 are sequentially formed on the first upper cladding layer 36 and the second upper cladding layer 37. As a method for forming the third upper cladding layer 38 and the first contact layer 39, for example, MOCVD can be used. For example, the third upper cladding layer 38 may be 1200 nm in thickness by using p-InP as a forming material. For example, the first contact layer 39 may be formed using p-InGaAs as a forming material and may have a thickness of 300 nm.

Next, as shown in FIG. 12, a patterned second mask layer M2 is formed on the first contact layer 39 using a technique such as photolithography. SiO ₂ was used as a material for forming the second mask layer M2. Then, using the second mask layer M2 as a mask, a region where the second mask layer M2 is not formed is removed by etching, and a mesa structure as shown in FIGS. 13 and 14 is formed. As an etching method, for example, ICP-RIE can be used. By this etching, a portion having a thickness of about 3 μm is removed from the surface to form a mesa structure. In addition, a part of the surface of the substrate 30 is also removed by this etching. FIG. 13 is an enlarged sectional view taken along line FF in FIG. 12 of the mesa structure forming the semiconductor laser. FIG. 14 is an enlarged sectional view taken along the line GG of FIG. 12 of the mesa structure forming the first optical waveguide. As shown in FIG. 12, the core layer forming the first bent optical waveguide is bent and formed in the same manner as the second mask layer M2.

  Next, as shown in FIGS. 15 and 16, a patterned third mask layer M3 is formed on the substrate 30 on which the mesa structure is formed using a technique such as photolithography. For example, SiN can be used as a material for forming the third mask layer M3. The region where the third mask layer M3 is formed will become the second buried region B2 in the future. Further, the third mask layer M3 is formed to cover the portion of the position P described with reference to FIG. 5 with respect to the mesa structure portion forming the first and second bent optical waveguides. That is, the third mask layer M3 is not formed on the mesa structure portion for forming the semiconductor laser and the portion on the semiconductor laser side from the position P of the mesa structure for forming the first and second bent optical waveguides.

  Then, as shown in FIG. 17, using the second mask layer M2 and the third mask layer M3 as a selective growth mask, the first buried layer is formed on the region where the second mask layer M2 and the third mask layer M3 are not formed. 42 is formed, and the mesa structure on the substrate 30 is embedded by the first embedded layer 42. As a method for forming the first buried layer 42, for example, an MOCVD method can be used. As a material for forming the first buried layer 42, for example, semi-insulating InP (SemiInsulating-InP) can be used. The portion where the first buried layer 42 is formed becomes the first buried region B1.

  Then, the second mask layer M2 and the third mask layer M3 are removed. These mask layers are removed using, for example, a hydrofluoric acid-based etchant.

Next, a first passivation layer 43 is formed on the entire surface of the substrate 30. As a method for forming the first passivation layer 43, for example, a CVD method can be used. As a material for forming the first passivation layer 43, for example, SiO ₂ can be used.

  Then, as shown in FIG. 18, the second buried layer 44 is formed on the first passivation layer 43, and the mesa structure of the second buried region B <b> 2 is buried with the second buried layer 44. As a method for forming the second buried layer 44, for example, a spin coating method can be used. In addition, as a material for forming the second embedded layer 44, for example, a low refractive index material such as benzocyclobutene (BCB) can be used. The substrate 30 on which the BCB is spin-coated is subjected to an appropriate heat treatment. Here, FIG. 18 shows a cross-sectional structure corresponding to the position shown in FIG.

  As shown in FIG. 19, the second buried layer 44 is also formed on the first buried layer 42 included in the first buried region B <b> 1 via the first passivation layer 43. FIG. 19 shows a cross-sectional structure corresponding to the position shown in FIG.

  Next, a second passivation layer 45 is formed on the entire surface of the substrate 30. As a method for forming the second passivation layer 45, for example, plasma CVD can be used. Further, as a material for forming the second passivation layer 45, for example, SiN can be used.

  Then, a patterned fourth mask layer M4 having an opening is formed in a region where the laser driving electrode and the first and second phase modulation electrodes are formed, and the fourth mask layer M4 is used to expose the opening. The second passivation layer 45 is removed by wet etching or the like. As a material for forming the fourth mask layer M4, for example, a photoresist can be used.

  Subsequently, the portion of the second embedded layer 44 exposed in the region where the laser drive electrode and the first and second phase modulation electrodes are formed is removed using dry etching such as ICP-RIE, The first passivation layer 43 is exposed. As a cross-sectional view in this state, FIG. 20 shows an enlarged cross-sectional view at a position corresponding to the line HH in FIG. 15, and FIG. 21 shows an enlarged cross-sectional view at a position corresponding to the line II in FIG. .

  Next, the portion of the first passivation layer 43 exposed at the opening of the fourth mask layer M4 in the region where the laser driving electrode and the first and second phase modulation electrodes are formed is removed using wet etching or the like. As a result, the first contact layer 39 having a mesa structure is exposed.

  Then, the first electrode 40 is formed on the entire surface of the substrate 30. The first electrode 40 is formed on the first contact layer 39 in the opening of the fourth mask layer M4 in the region where the laser driving electrode and the first and second phase modulation electrodes are formed. The first electrode 40 is formed as an Au / Zn / Au film, for example, using a vacuum deposition method. Then, the portion of the first electrode 40 formed on the fourth mask layer M4 is removed together with the fourth mask layer M4.

  Then, the second electrode 41 is formed on the entire surface of the substrate 30. The second electrode 41 is formed as a Ti / Pt / Au film by using, for example, a sputtering method. A mask pattern (not shown) having an opening in a region where the laser driving electrode and the first and second phase modulation electrodes are formed is formed on the second electrode 41. Then, using the second electrode 41 as an electrode, a conductive layer is plated on a portion on the second electrode 41 exposed at the opening of the mask pattern. Au can be used as a material for forming the conductive layer. Then, after the mask pattern is removed, the portion of the second electrode 41 in the region where the conductive layer is not formed is removed using dry etching or the like using the conductive layer formed by plating as a mask.

  Thus, the portion of the conductive layer plated in the region to be the laser drive electrode becomes the laser drive electrode, and the portion of the conductive layer plated in the region to be the first and second phase modulation electrodes is the first and second. It becomes a phase modulation electrode.

  In this way, the structure shown in FIGS. 1 to 4 and 6 is formed.

  Then, the back surface of the substrate 30 (the surface opposite to the surface on which the electrodes and the like are formed) is polished so that the thickness of the substrate 30 is about 150 μm, and is formed on the entire surface of the back surface by, for example, vacuum deposition. An AuGe / Au film is formed. Then, a mask pattern having an opening appropriately patterned using a photoresist is formed on the AuGe / Au film, and then Au plating is formed on the AuGe / Au portion exposed in the opening, so that the lower electrode is formed. It is formed. Thereafter, the substrate 30 from which the mask pattern has been removed is appropriately subjected to heat treatment, and contacts having good ohmic properties are obtained on the front surface and the back surface of the substrate 30 to complete the optical semiconductor device shown in FIG. .

  According to the optical semiconductor element 10 of the present embodiment described above, the semiconductor laser 11 and the semiconductor optical modulator are formed on the same substrate, and the dimensions are reduced. Specifically, since the optical semiconductor element 10 does not include the optical branching device included in the conventional semiconductor MZ optical modulator, the dimension in the longitudinal direction is reduced. Moreover, since the semiconductor laser 11 is disposed so as to be orthogonal to one end side in the longitudinal direction of the first phase modulation unit 12 and the second phase modulation unit 13, the size in the longitudinal direction is further reduced.

  Further, according to the optical semiconductor element 10, the number of elements that can be manufactured from one substrate is increased by reducing the longitudinal dimension.

  Furthermore, according to the optical semiconductor element 10, since the dimension in the longitudinal direction is reduced, the aspect ratio (aspect ratio) of the element is reduced, so that the yield in manufacturing the element is improved.

  Further, according to the optical semiconductor element 10, as described above, the branching optical branching device included in the normal MZ optical modulator is not necessary. Usually, the MZ optical modulator includes an optical branching device that branches input light into two optical waveguides. In order to obtain a high extinction ratio, it is desirable that the input light is branched at the same light intensity, with the light branching ratio at which the input light is branched into two optical waveguides being 0.5. When such a branching ratio is used, an off state in which light intensity is ideally zero is realized in an optical signal that is combined by the propagation light propagated through each optical waveguide. However, the MZ optical modulator has variations in the optical branching characteristics of the optical splitter due to variations in the manufacturing process, and the optical branching ratio at which the input light is split into the two optical waveguides deviates from 0.5. There is a case. Further, the optical branching device has a wavelength dependency with respect to the light branching ratio.

  On the other hand, since the optical semiconductor device 10 does not include an optical branching device that branches input light into two optical waveguides, the optical loss that can be generated by this optical branching device or the wavelength dependence of the branching ratio does not occur. There is no problem caused by the optical splitter.

  Further, according to the optical semiconductor element 10, the branching ratio of the light output to the first optical waveguide 12a and the second optical waveguide 13a is adjusted by adjusting the light intensity output from each of the opposing ends of the semiconductor laser 11. You can also The intensity of the output light can be adjusted by, for example, designing the internal structure of the semiconductor laser 11 or arranging a gain or loss region outside the semiconductor laser 11. In this way, the extinction ratio is improved by adjusting the light branching ratio. In addition, by adjusting the light branching ratio, a light loss difference that occurs during chirp control is compensated. In this way, the optical semiconductor element 10 improves the transmission characteristics.

  Further, according to the optical semiconductor element 10, by using the light output from each of the opposite ends of the semiconductor laser 11, the semiconductor laser can be compared with the case of using only the light output from one end of the semiconductor laser. 11 can be effectively utilized. Therefore, the power consumption of the semiconductor laser is reduced.

  Next, modifications of the optical semiconductor device of the first embodiment described above will be described below with reference to the drawings.

  FIG. 22 is a diagram illustrating a first modification of the optical semiconductor device according to the first embodiment.

  As shown in FIG. 22, in the optical semiconductor element 10 a of Modification Example 1, each of the first phase modulation unit 12 and the second phase modulation unit 13 includes a phase adjustment unit 23 formed on the substrate 30. The phase adjusting unit 23 is formed by a portion of the first optical waveguide 12a on the first bent optical waveguide 17a side, a portion of the second optical waveguide 13a on the second bent optical waveguide 17b side, and the phase adjusting electrode 23a.

  The phase adjustment unit 23 applies a voltage to the phase adjustment electrode 23a to change the phase of light propagating in the first optical waveguide 12a or the second optical waveguide 13a to the first phase modulation electrode 12b or the second phase modulation electrode. It can be controlled independently of the modulation by 13b.

  The width of the optical waveguide may be shifted due to processing accuracy. Due to such a displacement, a phase difference occurs between the light incident on the first optical waveguide 12a and the light incident on the second optical waveguide 13a.

  Therefore, in the first modification, the phase adjustment unit 23 is disposed in each of the first phase modulation unit 12 and the second phase modulation unit 13, and the light incident on the first optical waveguide 12a and the second optical waveguide 13a are incident. The phase difference from the light is adjusted.

  The arrangement of the phase adjusting unit 23 in each of the first phase modulating unit 12 and the second phase modulating unit 13 as in the optical semiconductor element 10a of the modified example 1 may be applied to other embodiments or modified examples thereof. good.

  In the first modification, the phase adjustment unit 23 is formed in the second embedded region B2, but the phase adjustment unit 23 may be formed in the first embedded region B1.

  Further, the phase adjustment unit 23 may adjust the phase of light by using a plasma effect by current injection.

  In the first modification, the phase adjustment unit 23 is disposed in each of the first phase modulation unit 12 and the second phase modulation unit 13. However, the phase adjustment unit 23 may be the first phase modulation unit 12 or the second phase modulation unit. You may arrange | position in any one of the modulation | alteration part 13. FIG.

  Further, the phase adjustment unit 23 may be disposed between each of the first phase modulation unit 12 and the second phase modulation unit 13 and the optical coupler 15.

  FIG. 23 is a diagram illustrating a second modification of the optical semiconductor device according to the first embodiment.

  In the optical semiconductor element 10b of Modification 2, the shapes of the first and second optical waveguides 12a and 13a are different from those of the first embodiment described above.

  That is, the first optical waveguide 12 a extends linearly from the end of the optical semiconductor element 10 on the semiconductor laser 11 side toward the end of the optical coupler 15 along the longitudinal direction, and then the optical semiconductor element 10. It extends obliquely inward in the width direction and is connected to the third bent optical waveguide 18a.

  The second optical waveguide 13 a is formed symmetrically with the first optical waveguide 12 a with respect to the central axis in the width direction of the optical semiconductor element 10.

  In addition, the shape of the shape of the 1st and 2nd optical waveguides 12a and 13a in the modification 2 and 1st Embodiment mentioned above is an example, and may have another shape.

  Next, optical semiconductor elements according to second to fourth embodiments disclosed in the present specification will be described below with reference to the drawings. Regarding points that are not particularly described in the second to fourth embodiments, the description in detail regarding the first embodiment is applied as appropriate. Further, in FIGS. 24 to 28, the same reference numerals are given to the same forming elements as those in FIGS.

  FIG. 24 is a diagram illustrating a second embodiment of the optical semiconductor element disclosed in this specification.

  The optical semiconductor element 50 of the present embodiment includes a gap between one end of the semiconductor laser 11 and the first phase modulation unit 12 and a gap between the other end of the semiconductor laser 11 and the second phase modulation unit 13. A gain adjusting unit 27 is provided that receives the output light from the semiconductor laser 11 and outputs the light after adjusting the intensity. The gain adjustment unit 27 is formed on the substrate 30 in the same manner as the semiconductor laser 11.

  The gain adjusting unit 27 includes a gain adjusting mesa unit 27a formed by extending the laser mesa unit 11a of the semiconductor laser 11, and a gain adjusting electrode 27b for injecting current into the gain adjusting mesa unit 27a. A diffraction grating is not formed in the diffraction grating layer 32 of the gain adjustment mesa portion 27a.

  The gain adjusting unit 27 increases the intensity of the output light of the semiconductor laser 11 by injecting a current into the gain adjusting electrode 27b. On the other hand, the gain adjustment unit 27 absorbs the output light of the semiconductor laser 11 and reduces the intensity of the output light by not injecting current into the gain adjustment electrode 27b.

  The optical semiconductor element 50 can adjust the intensity of each of the two output lights from the semiconductor laser 11 using the gain adjusting unit 27.

  The output light from the gain adjusting unit 27 is input to the first bent optical waveguide 17a or the second bent optical waveguide 17b.

  The optical semiconductor element 50 can perform chirp control using the gain adjustment unit 27 while ensuring a good extinction ratio. Hereinafter, chirp control using the gain adjusting unit 27 will be described with reference to the drawings.

  Optical signals transmitted over long distances are subject to waveform degradation under the influence of wavelength dispersion in the transmission path. For this reason, in the MZ optical modulator, in order to compensate for chromatic dispersion, a technique for suppressing degradation of the optical signal waveform after transmission by using chirp control that intentionally causes frequency fluctuation in the output light during modulation is used. ing. This technique is also called a pre-chirping method.

  In the optical semiconductor element 50, chirp control is performed, for example, by making the amount of phase change of propagating light propagating through the second optical waveguide 13a larger than that of propagating light propagating through the first optical waveguide 12a.

  FIG. 25 is a diagram illustrating the relationship between the phase modulation voltage, the phase change amount, and the loss amount.

As shown in FIG. 25, the magnitude of the second phase modulation voltage V ₂ applied to the second phase modulation electrode 13b is larger than the first phase modulation voltage V ₁ applied to the first phase modulation electrode 12b. The first phase modulation voltage V ₁ is an amplitude voltage V _pp and changes around the center voltage value. Similarly, the second phase modulation voltage V ₂ changes around the center voltage value with the amplitude voltage V _pp .

In the semiconductor optical modulator, since the refractive index change amount with respect to the modulation voltage, that is, the light phase change amount has a non-linear relationship, even if the amplitude voltage _Vpp is the same, the phase change of the light propagating through the second optical waveguide 13a The amount φ ₂ is larger than the phase change amount φ _{1 of} the light propagating through the first optical waveguide 12a.

  On the other hand, the amount of loss of light propagating through the optical waveguide increases as the value of the phase modulation voltage increases.

Therefore, as shown in FIG. 25, the loss amount α _{2 of} light propagating through the second optical waveguide 13a having a large phase modulation voltage value is larger than the loss amount α _{1 of} light propagating through the first optical waveguide 12a. Therefore, the extinction ratio may deteriorate due to chirp control.

  Therefore, in the optical semiconductor element 50, the intensity of light input to the second optical waveguide 13a in which the amount of loss of light propagating by chirp control increases is increased using the gain adjusting unit 27, so that the first optical waveguide 12a is By making it equal to the intensity of propagating light, a good extinction ratio can be secured.

  In this manner, the optical semiconductor element 50 can perform chirp control while ensuring a good extinction ratio.

  In the optical semiconductor element 50, the intensity of light input to the first optical waveguide 12a with a small amount of light loss due to chirp control is reduced by using the gain adjusting unit 27, and the light propagating through the second optical waveguide 13a. A good extinction ratio may be ensured by making it equal to the strength of.

When the first phase modulation voltage V ₁ applied to the first phase modulation electrode 12b is larger than the second phase modulation voltage V ₂ applied to the second phase modulation electrode 13b, the gain adjustment unit 27 is set. It is only necessary to increase the intensity of light input to the first optical waveguide 12a.

  Further, in the optical semiconductor element 50, even when chirp control is not performed, the gain adjusting unit 27 may be used in order to obtain a good extinction ratio by compensating for the delicate loss balance of the optical waveguide.

  In the optical semiconductor element 50, each of the first phase modulation unit 12 and the second phase modulation unit 13 includes a phase adjustment unit 23 formed on the substrate 30.

  Next, the manufacturing method of the optical semiconductor element 50 of 2nd Embodiment is demonstrated below.

  The optical semiconductor element 50 of the second embodiment can be manufactured in the same manner as the optical semiconductor element 10 of the first embodiment described above, except for the shape of the mask pattern used. Specifically, in the optical semiconductor element 50, a gain adjustment electrode and an auxiliary phase modulation electrode are added, and the shapes of the first and second phase modulation electrodes are different from those of the first embodiment. Therefore, if the mask pattern used for manufacturing the optical semiconductor element 10 of the first embodiment is appropriately changed, the second embodiment can be manufactured in the same manner as the first embodiment described above. Further, no diffraction grating is formed in the diffraction grating layer of the gain adjusting unit.

  In the optical semiconductor device 50 of the second embodiment described above, the gain adjusting unit 27 is disposed on both sides of the semiconductor laser 11. However, the gain adjusting unit may be disposed only on either one of the semiconductor lasers 11. good. Further, the gain adjusting unit may be arranged behind the first or second phase modulating unit.

  FIG. 26 is a diagram illustrating a third embodiment of the optical semiconductor element disclosed in this specification.

  The optical semiconductor element 60 of this embodiment includes a semiconductor laser 24 whose output light wavelength is variable. Specifically, as the semiconductor laser 24, a super structure grating (SSG) type DBR laser (hereinafter also simply referred to as SSG-DBR) is used.

  As shown in FIG. 26, the semiconductor laser 24 has a front DBR region 24a, a phase adjustment region 24b, a gain region 24c, and a rear DBR region 24d. The semiconductor laser 24 also includes a first drive electrode 24e that injects current into the front DBR region 24a, a second drive electrode 24f that injects current into the phase adjustment region 24b, and a third drive that injects current into the gain region 24c. An electrode 24g and a fourth drive electrode 24h for injecting current into the rear DBR region 24d are provided.

  The front DBR region 24 a, the phase adjustment region 24 b, the gain region 24 c, and the rear DBR region 24 d are arranged in series on the substrate 30. Similarly, the laser mesa portions forming the respective regions are arranged in series.

  The front DBR region 24a and the phase adjustment region 24b are integrally formed with a core layer. The core layer forming the rear DBR region 24d is formed of the same material as the front DBR region 24a and the phase adjustment region 24b. The front DBR region 24a, the phase adjustment region 24b, and the rear DBR region 24d are collectively referred to as a refractive index control region. The core layer of the gain region 24c is formed of a material different from that of the core layer of the refractive index control region.

  In the SSG-DBR type laser, a wide wavelength tunable operation can be obtained using the vernier effect by individually controlling the front and rear two DBR regions. Therefore, the optical semiconductor element 60 can output signal light at a plurality of wavelengths.

  As shown in FIG. 26, the first bent optical waveguide 17a extends in an arc shape from one end face of the rear DBR region 24d toward the first optical waveguide 12a. Similarly, the second bent optical waveguide 17b extends in an arc shape from one end face of the front DBR region 24a toward the second optical waveguide 13a.

  The output light from one side of the semiconductor laser 24 in the longitudinal direction is output to the first bent optical waveguide 17a from one end face of the rear DBR region 24d. Output light from the other in the longitudinal direction of the semiconductor laser 24 is output from one end face of the front DBR region 24a to the second bent optical waveguide 17b.

  In the optical semiconductor element 60, each of the first phase modulation unit 12 and the second phase modulation unit 13 includes a phase adjustment unit 23 formed on the substrate 30.

  Next, the manufacturing method of the optical semiconductor element 60 of 3rd Embodiment is demonstrated below.

  The manufacturing method of the third embodiment is the same as the manufacturing method of the optical semiconductor element 10 described above except for the method of forming the semiconductor laser 24. Therefore, the formation of the semiconductor laser 24 will be described below.

  The major difference between the method of forming the semiconductor laser 24 and the method of forming the semiconductor laser 11 in the method of manufacturing the optical semiconductor element 10 described above is that the core layer in the refractive index control region is grown by butt joint with respect to the core layer in the gain region 24c. And the fact that diffraction gratings are formed in the front DBR region 24a and the rear DBR region 24d, but no diffraction grating is formed in the phase adjustment region 24b and the gain region 24c.

  Specifically, in FIG. 6, after the core layer of the gain region 24c and the first upper cladding layer 36 are formed on the entire surface of the spacer layer 32, only on the region of the core layer where the gain region 24c is formed. A mask pattern is formed. Then, the first upper cladding layer 36, the core layer of the gain region 24c, and the spacer layer 32 in the region where the mask pattern is not formed are removed by etching. Then, a diffraction grating is formed using dry etching or the like in a portion of the diffraction grating layer 32 in a region where the front DBR region 24a and the rear DBR region 24d are formed. Then, the spacer layer 32, the core layer in the refractive index control region, and the first upper cladding layer 36 are formed in the region where the mask pattern is not formed, and the refractive index with respect to the core layer in the gain region 24c. The core layer of the control region is grown by butt joint. Then, a mask pattern is formed in the region where the semiconductor laser 24 is formed, and the core layer in the region where the mask pattern is not formed is removed by wet etching or the like. Then, the core layer 35 and the second upper cladding layer 37 of the optical waveguide are formed on the region other than where the semiconductor laser is formed. Subsequent steps are the same as in the manufacturing method described above. In addition, with respect to the formation of the drive electrode and auxiliary phase modulation electrode of the semiconductor laser 24 of the third embodiment, the mask pattern may be changed as appropriate.

  In the optical semiconductor element 60, the core layer of a passive optical waveguide such as a bent optical waveguide may be formed using the core layer in the refractive index control region.

  FIG. 27 is a diagram illustrating a fourth embodiment of the optical semiconductor element disclosed in this specification. FIG. 28 is an enlarged sectional view taken along line J-J ′ of FIG. 27.

  In the optical semiconductor element 70 of the present embodiment, the first phase modulation unit 12 and the second phase modulation unit 13 are arranged in series. The semiconductor laser 24 is arranged in parallel with the first phase modulation unit 12 and the second phase modulation unit 13 arranged in series. The semiconductor laser 24 is an SSG-DBR type laser as in the third embodiment described above.

  A gain adjusting unit 27 and a phase adjusting unit 23 are sequentially arranged in series on the outer sides of both ends in the longitudinal direction of the semiconductor laser 24. The gain adjusting unit 27 and the phase adjusting unit 23 are arranged in parallel with the semiconductor laser 24 and the first phase modulating unit 12 and the second phase modulating unit 13 arranged in series.

  The combined length of the semiconductor laser 24, the two gain adjusting units 27, and the two phase adjusting units 23 is substantially equal to the combined length of the first optical waveguide 12a and the second optical waveguide 13a.

  The output light from one end face in the longitudinal direction of the semiconductor laser 24 passes through the gain adjusting unit 27 and the phase adjusting unit 23 and is output to the first bent optical waveguide 17a. Similarly, the output light from the other end face in the longitudinal direction of the semiconductor laser 24 passes through the gain adjusting unit 27 and the phase adjusting unit 23 and is output to the second bent optical waveguide 17b.

  As shown in FIG. 27, the first bent optical waveguide 17a extends in an arc shape from the end surface of the phase adjusting unit 23 located on one side of the semiconductor laser 24 toward the first optical waveguide 12a. Similarly, the second bent optical waveguide 17b extends in an arc shape from the end face of the phase adjusting unit 23 located on the other side of the semiconductor laser 24 toward the second optical waveguide 13a.

  The core layer of the gain adjustment mesa portion 27a in the gain adjustment portion 27 is butt-joined with the core layer of the front DBR region 24a or the rear DBR region 24d. The core layer of the gain adjustment mesa portion 27a is formed of the same material as the core layer of the gain region 24c of the semiconductor laser 24.

  The core layer of the mesa structure in the phase adjustment unit 23 is butt-joined with the core layer of the gain adjustment mesa unit 27 a in the gain adjustment unit 27. The core layer having a mesa structure in the phase adjusting unit 23 is formed of the same material as the core layer in the refractive index control region of the semiconductor laser 24.

  The first bent optical waveguide 17a has a core layer that receives light from the input-side core layer and propagates the light to the output-side core layer by bending it.

  The part on the input side phase adjustment unit 23 side of the core layer forming the first bent optical waveguide 17a is formed integrally with the core layer of the phase adjustment unit 23 on the input side. On the other hand, the first optical waveguide 17a portion on the output side of the core layer of the first bent optical waveguide 17a is formed integrally with the core layer of the first optical waveguide 12a on the output side.

  As shown in FIG. 28, a junction interface S3 between the core layer 34a of the input-side phase adjustment unit 23 and the core layer 35 of the output-side first optical waveguide 12a is formed at a position in the middle of the first bent optical waveguide 17a. Is done.

  In the optical semiconductor element 70, the bonding interface S3 of the different core layers 34a and 35 is arranged at a position in the middle of the first bent optical waveguide 17a, and the semiconductor laser 24 passes through the first bent optical waveguide 17a by reflection at the bonding interface S3. The amount of light returning toward is reduced.

  Further, the joint interface S2 between the first buried layer 42 and the second buried layer 44 is disposed at a position in the middle of the first bent optical waveguide 17a, as in the first embodiment described above.

  In the optical semiconductor element 70, the second bent optical waveguide 17b is also formed in the same manner as the first bent optical waveguide 17a, and the above description regarding the first bent optical waveguide 17a is also appropriate for the second bent optical waveguide 17b. Applied.

  The third bent optical waveguide 18a receives the output light of the first optical waveguide 12a, bends the propagation direction, and propagates the light to the optical coupler 15. Similarly, the fourth bent optical waveguide 18b receives the output light of the second optical waveguide 13a, bends the propagation direction by 180 degrees, and propagates the light to the optical coupler 15.

  The fifth and sixth optical waveguides 19a and 19b are arranged in parallel with the second optical waveguide 13a and extend in the longitudinal direction of the second optical waveguide 13a.

  Next, the manufacturing method of the optical semiconductor element 70 of 4th Embodiment is demonstrated below.

  The manufacturing method of the fourth embodiment is the same as the manufacturing method of the optical semiconductor element of the third embodiment described above, except for the following points. Therefore, different points will be described below.

  The core layer of the gain adjusting unit 27 is formed simultaneously with the core layer of the gain region 24c of the semiconductor laser 24. The core layer of the phase adjusting unit 23 is formed simultaneously with the core layer in the refractive index control region of the semiconductor laser 24.

  Further, after the core layer of the refractive index control region is butt-joint grown with respect to the core layer of the gain region 24c, the region in which the semiconductor laser 24, the gain adjusting unit 27, and the phase adjusting unit 23 are formed and the first In addition, a mask pattern is formed on a portion on the phase adjustment portion side of the second bent optical waveguide (up to a portion where the bonding interface S3 in FIG. 27 is formed), and the core layer in a region where the mask pattern is not formed. Then, it is removed by wet etching or the like. The optical waveguide is formed on a region other than the region where the semiconductor laser 24, the gain adjusting unit 27, and the phase adjusting unit 23 are formed, and the region where the phase adjusting unit side portion of the first and second bent optical waveguides is formed. The core layer 35 and the second upper cladding layer 37 are formed. Subsequent steps are the same as in the manufacturing method described above.

  According to the optical semiconductor element 70 of the present embodiment described above, the size is reduced. Specifically, the first phase modulation unit 12 and the second phase modulation unit 13 arranged in series, and the semiconductor laser 24, the gain adjustment unit 27, and the phase adjustment unit 23 arranged in series are arranged in parallel. As a result, the dimension in the width direction is reduced.

  The position of the gain adjustment unit 27 and the position of the phase adjustment unit 23 may be interchanged. The gain adjusting unit 27 or the phase adjusting unit 23 may be arranged in series with the first optical waveguide 12a or the second optical waveguide 13a. Further, the optical coupler 15 and the fifth and sixth optical waveguides 19a and 19b may be arranged on the opposite side in the longitudinal direction of the optical semiconductor element 70 so that the output light is output from the opposite side.

  Like the optical semiconductor element 70, the optical waveguide core layer integrally formed with the input-side core layer and the optical waveguide integrally formed with the output-side core layer are provided in the middle of the first bent optical waveguide 17a. Arranging the bonding interface with the core layer may be applied to other embodiments or modifications thereof.

  Regarding the above-described embodiments, the following additional notes are disclosed.

(Appendix 1)
A semiconductor laser that is formed on the substrate and outputs light from each of the opposing ends;
A first phase modulation unit formed on the substrate and having a first optical waveguide to which output light from one end of the semiconductor laser is input;
A second phase modulator having a second optical waveguide formed on the substrate and into which output light from the other end of the semiconductor laser is input;
An optical coupler formed on the substrate and configured to combine and output output light from the first optical waveguide and the second optical waveguide;
An optical semiconductor device comprising:

(Appendix 2)
The semiconductor laser is formed on the substrate between one end of the semiconductor laser and the first phase modulator, or between the other end of the semiconductor laser and the second phase modulator. The optical semiconductor device according to appendix 1, further comprising: a gain adjusting unit that inputs the output light from the light and adjusts the intensity to output the light.

(Appendix 3)
The semiconductor laser has a first mesa portion embedded by a first embedded layer,
The first optical waveguide and the second optical waveguide are embedded by a second embedded layer having a refractive index smaller than that of the core layer of the first optical waveguide and the second optical waveguide,
Formed on the substrate, comprising a bent optical waveguide that inputs light and bends the propagation direction to propagate the light,
An input side portion of the bent optical waveguide is embedded by the first embedded layer, and an output side portion of the bent optical waveguide is embedded by the second embedded layer. 3. The optical semiconductor device according to appendix 1 or 2, wherein a bonding interface between the first buried layer and the second buried layer is formed at the position.

(Appendix 4)
A bent optical waveguide formed on the substrate, having a core layer that inputs light from the core layer on the input side, propagates the light to the core layer on the output side, and is bent;
The input side portion of the core layer of the bent optical waveguide is formed integrally with the input side core layer,
The output side portion of the core layer of the bent optical waveguide is formed integrally with the output side core layer,
The optical semiconductor element according to appendix 1 or 2, wherein a bonding interface between the input-side core layer and the output-side core layer is formed at a position in the middle of the bent optical waveguide.

(Appendix 5)
As the bent optical waveguide,
A first bent optical waveguide formed on the substrate and configured to input and bend the output light from one end of the semiconductor laser and to propagate the light to the first optical waveguide;
A second bent optical waveguide formed on the substrate and configured to input and bend the output light from the other end of the semiconductor laser and to propagate the light to the second optical waveguide;
The optical semiconductor element according to Supplementary Note 3 or 4, further comprising:

(Appendix 6)
The first phase modulation unit and the second phase modulation unit are arranged in parallel,
The optical semiconductor element according to any one of appendices 1 to 5, wherein the semiconductor laser is disposed on one end side of the first phase modulation unit and the second phase modulation unit that are disposed in parallel.

(Appendix 7)
The optical semiconductor element according to appendix 6, wherein a longitudinal direction of the semiconductor laser is in a direction intersecting with longitudinal directions of the first phase modulation unit and the second phase modulation unit arranged in parallel.

(Appendix 8)
The first phase modulation unit and the second phase modulation unit are arranged in series,
6. The optical semiconductor device according to claim 1, wherein the semiconductor laser is arranged in parallel with the first phase modulation unit and the second phase modulation unit arranged in series.

(Appendix 9)
The optical semiconductor element according to any one of appendices 1 to 8, wherein each of the first phase modulation unit and the second phase modulation unit includes a phase adjustment unit.

(Appendix 10)
The optical semiconductor element according to any one of appendices 1 to 9, wherein the semiconductor laser has a variable wavelength.

10, 50, 60, 70 Optical semiconductor element 11 Semiconductor laser 11a Laser mesa unit 11b Laser drive electrode 12 First phase modulation unit 12a First optical waveguide 12b First phase modulation electrode 13 Second phase modulation unit 13a Second optical waveguide 13b First Two-phase modulation electrode 15 Optical coupler 17a First bent optical waveguide 17aa First bent optical waveguide mesa 17b Second bent optical waveguide 18a Third bent optical waveguide 18b Fourth bent optical waveguide 19a Fifth optical waveguide 19b Sixth optical waveguide Waveguide 23 Phase adjustment unit 23a Phase adjustment electrode 24 Semiconductor laser 24a Front DBR region 24b Phase adjustment region 24c Gain region 24d Rear DBR region 24e First drive electrode 24f Second drive electrode 24g Third drive electrode 24h No fourth drive electrode 27 Gain Adjustment Unit 27a Gain Adjustment Mesa Unit 27 Gain adjustment electrode 30 Substrate 31 Lower cladding layer 32 Diffraction grating layer 33 Spacer layer 34 Core layer of semiconductor laser 35 Core layer of optical waveguide 36 First upper cladding layer 37 Second upper cladding layer 38 Third upper cladding layer 39 First contact Layer 40 first electrode 41 second electrode 42 first buried layer 43 first passivation layer 44 second buried layer 45 second passivation layer B1 first buried region B2 second buried region S1, S3 core layer junction interface S2 buried junction interface M1 first mask layer M2 second mask layer M3 third mask layer M4 fourth mask layer

Claims (6)

A semiconductor laser that is formed on the substrate and outputs light from each of the opposing ends;
A first phase modulation unit formed on the substrate and having a first optical waveguide to which output light from one end of the semiconductor laser is input;
A second phase modulator having a second optical waveguide formed on the substrate and into which output light from the other end of the semiconductor laser is input;
An optical coupler formed on the substrate and configured to combine and output output light from the first optical waveguide and the second optical waveguide;
An optical semiconductor device comprising:   The semiconductor laser is formed on the substrate between one end of the semiconductor laser and the first phase modulator, or between the other end of the semiconductor laser and the second phase modulator. The optical semiconductor device according to claim 1, further comprising: a gain adjusting unit that inputs the output light from the light and outputs the light after adjusting the intensity. The semiconductor laser has a first mesa portion embedded by a first embedded layer,
The first optical waveguide and the second optical waveguide are embedded by a second embedded layer having a refractive index smaller than that of the core layer of the first optical waveguide and the second optical waveguide,
Formed on the substrate, comprising a bent optical waveguide that inputs light and bends the propagation direction to propagate the light,
An input side portion of the bent optical waveguide is embedded by the first embedded layer, and an output side portion of the bent optical waveguide is embedded by the second embedded layer. 3. The optical semiconductor element according to claim 1, wherein a bonding interface between the first buried layer and the second buried layer is formed at the position of the optical semiconductor element. A bent optical waveguide formed on the substrate, having a core layer that inputs light from the core layer on the input side, propagates the light to the core layer on the output side, and is bent;
The input side portion of the core layer of the bent optical waveguide is formed integrally with the input side core layer,
The output side portion of the core layer of the bent optical waveguide is formed integrally with the output side core layer,
The optical semiconductor device according to claim 1, wherein a bonding interface between the input-side core layer and the output-side core layer is formed at a position in the middle of the bent optical waveguide. As the bent optical waveguide,
A first bent optical waveguide formed on the substrate and configured to input and bend the output light from one end of the semiconductor laser and to propagate the light to the first optical waveguide;
A second bent optical waveguide formed on the substrate and configured to input and bend the output light from the other end of the semiconductor laser and to propagate the light to the second optical waveguide;
An optical semiconductor device according to claim 3 or 4, further comprising: The first phase modulation unit and the second phase modulation unit are arranged in series,
6. The optical semiconductor device according to claim 1, wherein the semiconductor laser is arranged in parallel with the first phase modulation unit and the second phase modulation unit arranged in series.

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